Stereoscopic method and apparatus



NOV. 10, 1942. c w C R STEREOSCOPIC METHOD AND APPARATUS Filed July 7,1958 4 Sheets-Sheet l IN V EN TOR.

BY ATTORNEY .Nov. 19, 1942. c w CARNAHAN STEREOSGOPIC METHOD ANDAPPARATUS Filed July 7, 1958 4 Sheets-Sheet 2 INVENTOR.

Nov. 10, 1942. c. w. CARNAHAN Nml. 10), 1942. c w CARNAHAN 2,301,254

STEREOSCOPIC METHOD AND APPARATUS Filed July 7, 1958 4 Sheets-Sheet 4WWW WWW

IN V ENTOR.

BY %F iaA ATTORNEY Patented Nov. 10, 1942 2,301,254 s'raanoscorro METHODAND APPARATUS Chalon W. Carnahan, St. Marys, Pa., assignor to SylvaniaElectric Products Inc., a corporation of Massachusetts Application July7, 1938, Serial No. 217,866

22 Claims.

This invention relates to stereoscopic systems and more especially tosystems for projecting or reproducing images stereoscopically.

A principal object of the invention is to provide a method of recordingand receiving a stereoscopic view of a televison subject on a singlesurface.

Another principal object of the invention is to provide an improvedtelevision reproducing screen for reproducing television imagesstereoscopically or with apparent relief.

A feature of the invention refers to an improved method and apparatusfor scanning a televised scene or subject.

Another feature of the invention relates to a television reproducingscreen made up of a phirality of strips of dichroic polarizing material,alternate strips acting on the light passing therethrough to polarize itat right angles to the polarization of the light passing through theintervening strips.

Another feature relates to a television system comprising a linestructure of metallic coating On adjoining surfaces of two prisms joinedtogether by a cement of the same refractive index as that of thematerial of which the two prisms are made.

A further feature relates to a method of reproducing or projecting astereoscopic television image on a large screen.

A still further feature relates to the novel organization, relativelocation and interconnection of parts whereby an improved stereoscopictele- Vision system is produced.

Other features not specifically enumerated will be apparent after aconsideration of the following detailed descriptions and the appendedclaims.

While the invention will be disclosed herein as embodied in a typicaltelevision system applying cathode-ray tubes with or without theapplication of intermediate films, it will be understood that this isdone merely for explanatory purposes and not by way of limitation.Accordingly other well-known forms of television methods, as thesupersonic wave method or mechanical methods with rotating or vibratingmirrors or with perforated discs may be adapted to the application ofthe invention.

In the drawings, Fig. 1 represents an improved method of providingalternate operating and off voltages for two television transmittingcathoderay tubes according to one feature of the invention.

Figs. 2, 3 and 4 are wave diagrams explanatory of the method ofoperation of certain parts of Fig. 1. I

Fig. 5 is a schematic diagrammatic representation of a televisionreproducing arrangement according to the invention.

Fig. 6 illustrates the method of making the dichroic screen made up ofstrips polarizing the transmitted light alternately inplanes paralleland at right angles to the direction of the strips.

Fig. '7 shows a method of recording two stereoscopic views of the samescene or object at the transmitting end, either on a photoelectricscreen of a cathode-ray transmitting tube or on an intermediate movingpicture film.

Fig. 7a is an enlarged view of part of Fig. 7.

Fig. 8 shows an alternate method of reproducing a stereoscopic pictureof a televised scene or subject adapted to the use of a televisionprojection system.

Fig. 9 illustrates the method of applying either sequential orinterlaced scanning in connection with the invention.

The record of the original image may be produced either on a film or onthe photo-sensitive cathode of an iconoscope or an image dissector.

Fig. 7 shows one preferred method of forming this record for televisiontransmission. A coating of metallically reflecting lines 65 is depositedon the surface of prism 59. The part of the recording system shown inthe figure acts as a synthesizer on recording surface 64, of the twostereoscopic views of the object 54 as seen by the objective lenses 55and 56. Surface 64 may be either a photographic film or the screen of an"iconoscope or similar television scanner. The light rays L enteringthrough objective 55 are totally reflected at surface 66 of prism 51 anda part L1 is reflected by the metallized line structure 65 on prism 59through the end surface 61 of prism on to the recording surface 64. Theprisms 59- and 60 are cemented together by a transparent cement of thesame refractive index as that of the glass of which the prismsthemselves are made. Therefore, that part of the light rays L2 whichpasses between the metal strips is not reflected but passes through in.

the direction it arrived at the surface 65 until it meets the wall 63 ofprism 59. Here th light rays L; are absorbed by the black coating 63.The light rays L1 arriving at the recording surface 64 reflected by themetallic line structure produce an image of a line structure similar andparallel to that on surface 60.

The space left between theilluminated lines just described is filled inon recording surface 64 by that part R1 of the light rays R enteringthrough objective 56 from the object 54 in a way similar to thatexplained in detail for the light rays L. In this way the two views asseen by the two objectives are projected on the surface 64 as aninterleaved line structure.

If the recording surface 64 is the light sensitive screen of acathode-ray tube the line structure is scanned, preferably but notnecessarily by the interlaced scanning method.

An arrangement similar to the one described above is used, according tothe invention, in reproducing at the receiving end, say for projectionfrom a projection type cathode-ray tube. The interleaved image at thefluorescent screen of this tube is first separated by the prisms intothe two original images, the separated images are transmitted throughtwo dichroic filters, which are oriented at right angles to each otherwith respect to their polarizing properties, then combined again at theviewing screen in the same interleaved manner as explained above for therecording. The large screen picture obtained in this manner is observedby the audience by means of spectacles 5| (Fig. 5), in which dichroicscreens polarizing at right angles to each other admit to each eye onlythe correlated image of the interleaved surface on the screen, which isproper for the respective eye for producing the stereoscopic view of theoriginal scene. Fig. 8 illustrates the projection stereoscopically froman intermediate film record similar to the record 64 (Fig. 7). Therectangle R. in this figure represents schematically the apparatus ofFig. 7. Light from the source 68 is made parallel by the lens 69 andpassed through the film 10 on which the interleaved positive picture ofthe original subject or scene is printed. The light rays passing throughthe set of alternating strips on the film on which, say, the view of theobject 54 as seen by the objective 55 is printed, is guided by prismsI9, 80 and 11 through lens I2 and dichroic screen N, which has theproper orientation with respect to its polar properties corresponding tothe orientation of one of the dichroic screens, say, 52 of thespectacles worn by the observers. The strip picture projected with lightpolarized by dichroic screen 14 arrives at the projection screen 16. Thelight passing through theother set of strips in the film is guidedsimilarly by prisms I9 and 18 through lens 13 and dichroic filter 15 tothe viewing screen 16. The polar orientation of the filter I5 is atright angles to that of filter 14. In this way the image at the screen16 is built up of bands or strips of which one set of alternate onesreflects light polarized at right angles to that of the other set ofstrips. The distribution of the two sets of polarized images between theright and left eye of the observer is finally carried out by thedichroic screens .52 and 53 in the goggles as described above. Thescreen 16 is preferably of such material and surface structure by reasonof which the polarization of the reflected light is substantiallymaintained in the same plane as the incident light, at least forreflection through an angle of about 20 degrees from the normal to thesurface of the screen.

For reception on a direct viewing fluorescent screen, an alternatemethod is used according to the invention, in which the fluorescentscreen on the cathode-ray receiving tube is equipped with a dichroicfilter, make up of parallel stripes, passing alternately, horizontallyand vertically polarized light. The manufacture of this type ofstriped'filter will be described later.

Either sequential or interlaced scanning may be applied in connectionwith the described system of stereoscopic television. The scanning atthe transmission end must follow the lines of the image produced by thetwo objectives. At the receiving end, it has to follow the lines of thestriped dichoric filter, in case of cathode-ray tube projection ordirect viewing cathode-ray tube for reception, the scanningcorresponding to the one used in transmission is applied in the exposureof the positive film.

The choice between the two systems of scanning is immaterial in thesystems described above, and the selection between the two may be madeaccording to convenience. Interlaced scanning is preferred, according tothe invention, if it is desired to record the two images at thetransmitting end with two cathode-ray transmitting tubes rather thanwith one. The application of two tubes in place of one may beadvantageous at the transmitting end with the light available from theoriginal scene or subject to be televised is very weak.

In the system described above, viz. in the "prism system with themetallically reflecting line coating, more than half the light that isavailable for transmitting is lost in the prism system. As explained indetail above, this is due to the fact that in addition to the lossesfrom rejecting one half of the light arriving at the metal coated linestructure, there are losses in the glass prism due to absorption andsome reflection at the intersurfaces.

As is well known, the two stereoscopic views of an object may be takenon two entirely separated surfaces, as is usually done in conventionalstereoscopic photographs, say, side by side. When this principle istransferred to the two mosaic screens of, say, two iconoscopes, it isevident that means have to be provided to alternately bias the twoiconoscopes for oil and on operating conditions. The alternating biaswhich must be provided must be a very good approximation to arectangular time voltage curve, as the reproduced picture will otherwiseshow an undesirable increase of brightness along the lines. Furthermore,there is a maximum frequency which can be transmitted by anytransmission and amplifier system, and it is, therefore, desirable, toemploy the lowest available frequency for the fundav mental frequency ofthe rectangular voltage time curve. If this is done, the approximationto the rectangular shape of this curve is relatively better than withany higher fundamental frequency, because of highest frequency which canbe passed by the system is a higher harmonic of the fundamental. As iswell known from the theory of Fourier series, a sharp change indirection requires these high harmonics.

reception. If a second intermediate film i used (is In the arrangement,according to the invention cribed below, these two requirements arefulfilled by using a multivibrator and by the application of interlacedscanning.

manner, it .is preferred, in accordance with the invention, to employ apair of grid-controlled tubes which are arranged to pass platecurrent atregularly recurrent spaced intervals, one tube being blocked while theother tube is passing current.

Thus as shown in Fig. 1, the television impulses generated by dissectorl are applied to the control-grid 4 of a suitable grid-controlled tube-5which is preferably, although not necessarily, of the screen grid typecomprising an electronemitting cathode 6, a control-grid t, a shieldgrid1 and a plate electrode 8. Likewise the television impulses fromdissector 2 are applied to the control-grid 9 of a similargrid-controlled tube ill having an electron-emitting cathode H, acontrol-grid 9, a shield-grid l2, and a plate electrode E3. The grid lis connected to cathode 6 through the grid-biassing resistors M, It andthence to ground through the steady D. C. biassing source it, it beingunderstood that the oathode 6 is grounded as indicated. A similargridbiassing circuit is provided for tube ill traceable from the grid 9through bias resistors ll, 88,

biassing source it to ground, the cathode i i likewise being grounded.The plate electrodes ii and i3 are connected to a suitable source of asteady plate potential it through. a resistor 20. The shield-grids i andi2 are connected to an intermediate point of the D. 0. supply source l9through suitable resistors 2 i 22 in the wellknown manner. Theparameters of the above described grid-biassing circuits for each of thetubes 5 and iii, are chosen so that normally both tubes are classed totheir plate current cut-off. In order to render the tubes 5 and lilalternately effective in passing plate current, there is provided a pairof grid-controlled tubes 23, 2t, which are interconnected with a sourceof alternating current 25 by a multivibrator circuit arrangement. Forthis purpose, the plate electrodes 26,27, are connected through theirindividual resistors 28, 29, to a source of steady plate potential 30.The control-grids M, 32, are connected to their respective cathodes 33,34 through leak resistors 35, 36. The plate 25 is connected throughcondenser 37 to control-grid 32 and plate 2! is likewise connectedthrough condenser 38 to control-grid M. The controLgrid Si is alsoconnected through condenser 39 to the alternating current source 25.

In case of sequential scanning as distinguished from interlacedscanning, source 25 may be synchronized with the line frequency ofdissector l and 2 so that source 25 produces a signal at onehalf of theline scanning frequency. The plate 26 of tube 23 is connected throughcondenser 60 to a point between the resistors l t and It. Likewise theplate 25 is connected through condenser ii to a point between theresistors ll and 88. By reason of the multivibrator connection betweenthe source 25 and the tubes 23, 24, these latter tubes are alternatelyeffective in passing plate currents. In other words, the voltageconditions on the plates 23 and 21 are 180 out of phase as representedrespectively by the curve A of Fig. 2 and the curve B of Fig. 3 and thefrequency of the waves A and B is one-half of the line scanningfrequency represented by curve of Fig. 4. Consequently, the potential ofthe points i2, 43, will likewise be 180 out of phase. Likewise, thebiassing potential on the grids 6 and 9 at any given instant, will bedetermined by the biassing circuits above described as well as by thepotential applied through the condensers M, M. Therefore when grid 8 isbiassed below cut-off, the grid 9 is biassed above cut-off. Consequentlytube 5 will pass the amplified television currents from dissector I tothe amplifier M during a given I scanned line of the subject 3, and whenthe next 7 line of the subject 3 is scanned by device 2, the tube i0 isblessed below cut-off and the tube 5 is blessed above cut-01f so thatthe amplified output of tube alone is applied to the amplifier it. Bythis arrangement therefore, the devices 1 and 2 can scan the subject 3continuously, however, the impulses from the devices I and 2 arealternately eflective in controlling the amplifier 34 and since thealternations are synchronized with the line scanning frequency, the netresult is that one linear element of the subject 3 is scanned and itsresponse is amplified by tube 5, the next linear element is scar'med bydevice 2 is amplified by tube l0, and so on until all the linearelements of the subject are scanned. It will be understood of coursethat the television scanners are adjustable so that the width of thescanning spot of each scanner is equal to the width of each interleavedstrip of'the stereoscopic record being scanned and the number of linescanning traverses of the scanners is equal in length and number to thelength and number of each of the stereoscopic views of the record.

Preferably, and in accordance with the invention, source is synchronizedby the frame frequency rather than by half the line frequency, andinterlaced scanning is applied rather than sequential scanning. Thisinsures, as explained above, an improved approximation to therectangular shape of the voltage time curve for the ofi and operatingbias of the two iconoscopes.

After suitable amplification in the amplifier M, the television currentsmay be transmitted over any well-known transmission channel such as awire channel, a radio channel or the like to any well-known form oftelevision receiver indicated schematically in Fig. 5 by the numeral 65.For the details of such a receiver, reference may be had to Fender andMcIlwain, Electrical Engineers Handbook, third edition, V, l5-25, JohnWiley 8; Sons, New York, 1936.

In the well-known manner, the output of the receiver is used to controlthe production of a light spot of varying intensity and this spot ismoved over a suitable reproducing screen in synchronism with thescanning spots of the devices I and 2 at the transmitter. For purposesof iilustration, the device for producing the moving light spot in Fig.5 is represented schematically by a cathode-ray tube 46 by means ofwhich the received television currents are converted into the originalimage on the end wall or screen A! of the tube. Ordinarily, the image onthe screen 41 would be viewed by an observer directly. In accordancewith the present invention, the light image reproduced on screen M isprojected or passed through another screen 68 made up of a plurality ofsuccessive linear strips 49, 50, of any well-known dichroic lightpolarizing material, such as for example as Polaroid. It will beunderstood of course that there will be the same number ofstrips 49, 50,as the number of linear elements scanned in the original subject.

The strips 69 and are arranged sothat alternate strips polarize thelight passing therethrough at right angles, for example the strips 49may be arranged to polarize horizontally the light passing therethrough,while the strips 50 polarize vertically the light passing therethrough.The observer views the screen 48 through a pair of dichroic lightpolarizing filters which may, for example be mounted in a'spectacleframe 5|. The filter 52 mounted in the left portion of the spectacleframe is arranged to pass light polarized in a horizontal plane, thatis, the light passed by strips 49; while the filter 53 in the righthandpart of the spectacle frame passes light polarized in the verticalframe, that is, the light passed by strips 50. It'will be understood ofcourse, in accordance with well-known television principles, that thecomplete subject at ithe transmitter and at the receiver is scanned acertain minimum number of times per second in accordance with thepersistency of vision, for example, the subject may be scannedcompletely sixty times per second. Consequently, the observer viewingthe screen 48 through the filters 52, 53, sees the image first throughone eye and then through the other. Because of these displaced images,corresponding to the 'scannings by devices I and 2 at the transmitterwhich are stereoscopically or angularly placed with respect to thesubject 3, the observer is given the impression of depth or relief inthe. image reproduced screen 43. It will be understood that the numberof linear elements scanned and consequently the number of strips 49, 50,employed in the reproducing section are such that each alternate set ofstrips when' illuminated givea satisfactory complete image of thesubject.

The dichroic screen 48 of which alternate strips 49 and 50 are passinglight polarized parallel and at right angles respectively to thedirection of the'strips may be made in a number of ways. A preferred waywill now be described in connection with Fig. 6.

Generally, the proper orientation of the dichroicmaterial to secure ahigh and uniform degree of plane polarization of the transmitted lightis accomplished by using some asym-.

. metrical property of the material to align the particles. If theasymmetry is one of physical dimensions, e. g. as in the crystals ofherapathite, which are needle shaped, the unoriented crystal mass mixedin a viscous cellulosic matrix may be extruded through a long narrowtube causing the needle-like crystals to be aligned in the direction ofthe fiow lines of the matrix. If the asymmetric property is a largemolecular magnetic or electric moment, the mixture of dichroic materialand matrix either during or after deposition on the supporting base, issubjected to suitably directed magnetic or electric fields,whichinteract with the individual molecular moments to align thecrystals in'the preferred direction with respect to the fields.Generally, dichroic materials show all of the above mentionedproperties, and alignment by liquid fiow is to be preferred because ofits greater convenience.

One way of making the screen 48 would be to cut e. g. the strips 49parallel to the direction of flow of one sheet of dichroic materialdeposited on :Sat surface by the flow method described above. The strips50 may then be cut out of another sheet at right angles to the lines offiow. Finally alternate strips are cemented parallel to and touchingeach other on a suitable transparent carrier plate.

Considering the narrowness of the strips, which is of the order of .008"to .040", the cutting andcementing of a screen according to thedescribed method may be inconvenient. According to the invention,therefore, one sheet 82 of the liquid dichroic material is deposited(see Fig. 6) on a suitable transparent matrix 8| provided withrectangular grooves of the desired width and distance between thegrooves, from the nozzle 84. This sheet is deposited parallel to thedirection of the grooves. A sheet 82 of periodically variable thicknessviz. of the thicknesses AB and AC respectively is thus formed on thematrix 8|. Before or after the dichroic material has dried, the layerthickness AB is removed leaving the grooves 83 filled with the polarizedmaterial, while the strips between th grooves are free from,

dichroic material. The second half of the dichroic linear screen is madeby depositing in a similar way on a matrix 8| dichroic material from anappropriate nozzle, this time, however, at right angles to the directionof the grooves in the matrix. After removing the excess material asbefore on the first half, the two halfscreens are cemented together inthe manner indicated in Fig. 6.

What I claim is: V

1. In a stereoscopic system, means to form an interleavedstereoscopicrecord of an image com-' prising a prism having one,face provided with aplurality of spaced linear reflecting strips, means to form two separatesterecsccpic views of the image,- means to project one of said views onsaid prism face at such an angle that only spaced linear elements arereflected by said reflecting strips, and means to transmit the other ofsaid views through the spaces between said strips, a receiving surface,and means to project upon said surface the reflected image strips and-the transmitted image strips to form a single interleaved stripstereoscopic image.

2. A system according to claim 1 in which television scanning means areprovided to scan said interleaved image on said receiving surface.

3. A system according to claim 1 in which the said means on the said oneof said prism faces consists of a series of spaced metallic reflectingstrips.

4. A system according to claim 1 in which television scanning means areprovided to scan said interleaved image and the width of the scanningspot of the television scanner is adjustable to the width of each of theinterleaved strips of the image.

5. A stereoscopic system comprising a prism having alternate linearstrips which are light transmitting and light reflecting, means toproject upon said strips corresponding sets of light strips each set oflight strips representing a corresponding stereoscopic spaced-stripimage of a single subject whereby av single complete view of the subjectis broken up into two simultaneous specially separated views eachcorresponding to one of said sets of light strips, and means to passlight simultaneously from said separate views through respectivedichroic filters arranged to polarize in mutually perpendicular planesthe light passing therethrough.

6. A stereoscopic system according to claim 5 in which the polarizedlight passed by said filters is projected on a screen having a surfacewhereby the light reflected therefrom is maintained in substantially thesame polarized plane as the incident light at least for reflectionthrough an angle of 20 degrees from the normal to the surface thereof.

7. A system according to claim 1 in which said receiving surfaceconsists of a viewing screen, said screen having associated therewithdichroic polarizers for producing a single stereoscopic image on saidscreen with alternate strips having the light polarized in one plane andthe intervening strips having the light polarized in a plane at rightangles to said one 'plane.

8. In a stereoscopic system, means to form a single interleaved stripstereoscopic record repand passing the polarized lights throughcorreresenting different stereoscopic aspects of an image comprising apair of prisms having opposed surfaces cemented together by a cement Ihaving the same refractive index as that of the prisms, means disposedon one of said cemented surfaces for composing an interleaved stripimage of two separate stereoscopic views of a subject or scene, andmeans to project said single interleaved image on a receiving surface.

9. In stereoscopic television apparatus, means to form two separateimages representing spaced stereoscopic views of a subject and tocombine said views into a single interleaved strip view, a televisionscanner for scanning each of said interleaved strips, and meansincluding a single television reproducer and a dichroic filter screenfor reproducing said image stereoscopically. I

l0. Apparatus according to claim 9 in which the television reproducerincludes the fluorescent screen of a cathode-ray tube.

11. In a stereoscopic apparatus comprising means for forming twoseparate stereoscopic views representing different aspects of a subjectand combining them including a prism, having on one face' a series ofspaced reflecting strips, means to project on said reflecting strips oneof said separate views for reflecting only alternate lines, means totransmit only alternate lines of the other view through the spacesbetween the said reflecting strips, and a single receiving surface uponwhich the transmitted and reflected lines are simultaneously projectedand interleaved to form a single image.

12. Stereoscopic apparatus including means to form on the photo-cathodeof a cathode-ray tube television transmitting scanner a singlestereoscopic interleaved strip image of a subject, means to scan saidinterleaved strip image to produce television currents representingthetwo interleaved stereoscopic images and means to reproduce an image ofthe subject under control of said currents the last-mentioned meansincluding a single cathode-ray receiving tube having a dichroic filterscreen associated therewith, said fllter having interleaved stripscorresponding to said interleaved strips of the original stereoscopicimage certain of said filter strips polarizing light in one plane, andother of said strips polarizing light in another plane.

13. Stereoscopic television reproducing apparatus comprising acathode-ray tube television receiver, a screen associated with saidreceiver comprising alternate strips of dichroic material each stripcorresponding to a corresponding strip of the fluorescent screen of saidtube and alternate strips polarizing light received thereby in a planeat right angles to the polarization of the light received by theintervening strips.

14. The method of electro-optical transmission which includes the stepsof scanning a television scene to produce two series of current impulsesrepresentative of stereoscopic views of the subject, translating thecurrents into a corresponding television image, polarizing the lightfrom alternate strips of said image in one plane and polarizing thelight from the intervening strips in a diflerent plane, and passing saidpolarized light through corresponding polarized viewing filters.

15. The method of electro-optical transmission which includes the stepsof projecting a received television image on a light polarizing screento divide certain elements of the image into light polarized in oneplane and to divide other elements into light polarized in a differentplane.

sponding polarized filters.

16. Means for reproducing a television image stereoscopically comprisinga screen upon which the television image is projected, said screenconsisting of a plurality of sets of dichroic light polarizing memberscertain of said members polarizing in one plane light from correspondingareas of the image and other dichroic members polarizing light fromother corresponding areas of the image in a difierent plane, and a pairof light filters, each filter passing light from only one of said setsof members.

1'7. The method of producing a stereoscopic image of a subject whichincludes the steps of producing on two separate reflectors separatecomplete images of the subject, reflecting said separate images on to acommon reflector having alternate linear light reflecting and lighttransmitting strips, to produce a single composite stereoscopic image ona receiving surface which image consists of alternate interleaved linearstrips.

18. The method of producing a stereoscopic image of a subject whichincludes the steps of projecting the image on to a surface havingalternate linear light reflecting and light transmitting strips, passingthe light reflected from the reflecting strips through a correspondinglypolarized light filter passing the light transmitted by said lighttransmitting strips through another correspondingly polarized lightfilter, and projecting the lights passed by said filters in superposedrelation on a receiving surface.

19. Apparatus for producing a stereoscopic image of a subject comprisingmeans to produce two complete stereoscopic images of the subject, aprism having one of its faces provided with alternate linear lightreflecting strips and light transmitting strips, means to project saidcomplete images on said prism face so that the light from alternatestrips of one of said complete images is reflected from said lightreflecting strips and the light from the alternate strips of the otherof said complete images is transmitted through said light transmittingstrips, and a receiving surface upon which the reflected strips andtransmitted strips are interleaved to form a single compositestereoscopic image.

20. Apparatus according to claim 19 in which said rism is formed of twoprism sections having opposed surfaces together cemented together with acement having the same refractive index as that of the prisms.

21. An arrangement for forming an interleaved stereoscopic image of asubject comprising a pair of prisms cemented together, the opposing faceof one prism being rovided with spaced linear light reflecting strips,and means to project upon said face a single image representing spacedstereoscopic views of the subject.

22. The method of electro-optical transmission which includes the stepsof scanning a television scene to produce television currentsrepresenting an interleaved-strip stereoscopic views of a subject,translating the currents into a corresponding television image,polarizing the light from alternate strips of said television image inone plane and polarizing thelight from the intervening strips of saidtelevision image in a different plane, and passing said polarized lightfrom all of said strips through corresponding polarized viewing filters.

CHALON W. CARNAHAN.

